In the prior art, non-diffraction limited laser beams from high power laser sources often have to be transported from a laser source to a remote location that is many feet away. Passive silica fibers are normally used for transporting laser light from its source to the remote location. Passive silica fibers are also used for connecting components in fiber-optic devices, such as interferometers and fiber lasers. They then play a similar role as electrical wires do in electronic devices.
However, traditional passive silica fibers are lossy, especially over long lengths. The beam quality can be made better but it is at the expense of a power loss. In addition, traditional multi-mode passive fibers make a laser beam more highly moded which also affects system performance, particularly if only one mode is desired. To solve these problems the prior art has required that relatively complex and costly optical amplifiers and other optical equipment be utilized to amplify and restore degraded laser beams.
In addition, when high power laser beams are generated for transmission through ordinary passive silica fibers, which typically carry single mode beams, the limitations in the amount of power a single fiber can carry requires that multiple apertures and multiple fibers be utilized. The source laser beam must be divided and is routed through each fiber before recombining them. The multiple fibers are typically small diameter single-mode fibers. Accomplishing this is somewhat complex and costly to implement.
In addition, efficiently launching laser light into single-mode fibers usually requires a laser source with good beam quality and precise alignment of the focusing optics in order to achieve mode matching. This requires more complex and costly components. As described below, compact solid state lasers typically have poor beam quality so are not acceptable for this purpose. Thus, small single-mode fibers generally are not useful as transport fibers carrying laser light from high power solid state lasers.
To get around this problem large core fibers are usually utilized but large-core fibers tend to be multimode which degrades the beam quality. This occurs because the number of transverse modes and higher order modes supported by a fiber is proportional to the core diameter. The multimodes include a primary mode that is of interest, and many transverse and higher order modes that may not be of interest. The unwanted modes take some of the power that is generated by the high power solid state laser that is driving the transport fiber and thereby decrease the efficiency at the primary mode of interest.
Further, working with high power solid state lasers, many of them are not diffraction-limited and this results in a coupling loss into the passive fibers which typically transport single-mode beams. These fibers can be designed to accept multimode light, but the output from the fiber will be multimode as well which is not wanted.
When compact (small or short), high power, solid state lasers are utilized, when mounting space is small, other problems exist. Mainly, as previously mentioned, the beam quality from these compact solid state lasers begins to degrade. However, from a favorable standpoint such compact solid state lasers save weight, are smaller, can generate favorable power and have good spectral and/or temporal characteristics. Such solid state lasers are typically diode pumped in a manner known in the art.
Thus, there is a need for a way to transport laser beams output from a compact, high power, solid state laser that alleviates the above described beam quality and loss problems in the prior art in a simple and cost effective way.